Method of reshaping passageways in metal strip-type tubing

ABSTRACT

A method and apparatus for producing a metal strip-type tubing having a first surface and an opposing surface of the tubular passageways flattened. The flattened surfaces are obtained by passing the tubing through a deforming means such as spaced apart rolls. It is essential that the edges of the strip-type tubing be restrained during the flattening operation. The apparatus includes means for deforming the flats on the strip-type tubing and means for restraining the edges of the flats during the deforming operation. The resulting tubular passageways have a polyhedral cross section which is adapted to be bonded to the flat type fin stock. The resultant tubing and heat exchangers formed of the tubing is also part of the invention.

Unlted States Patent 1 1 1 1 5 Tranel 1 *Oct. 8, 1974 METHOD OFRESHAPING PASSAGEWAYS 2,998,639 9/1961 Forst a 211....v 29/1573 v [NMETAL STRHLTYPE TUBING 2,999,304 9/1961 Pauls 3,067,491 12/1962 Neel eta1. Inventor: Lester J- Tranel, is, o 3,196,657 7/1965 Fromson 29/1573 Rx Assignfiez Olin corporafion, New Haven, 3,735,720 5/1970 Tranel29/1573 D Conn. FOREIGN PATENTS OR APPLICATIONS 1 Notice; The portion ofthe term of this 702,086 1/1965 Canada 29/1573 V patent subsequent toMay 29, 1990, has been disclaimed. Primary Examiner-Charles W. LanhamAssistant Examiner-D. C. Reiley, III [22] 1972 Attorney, Agent, orFirm-Robert H. Bachman [21] Appl. No.: 247,606

Related US. Application Data 1 ABSTRACT [62] Division of Ser. No.122,607, March 1, 1971, A method and apparatus for producing a metalstripabandonedtype tubing having a first surface and an opposing surfaceof the tubular passageways flattened. The flat- 1 1 118 -3 9/ 7-3 Vtened surfaces are obtained by passing the tubing [51 Int. Cl BZld53/02, 323p 15/26 through a deforming means such as spaced apart rolls,1 Field of Search It is essential that the edges of the strip-typetubing be /1 157-3 .3 D; 113/118 R, restrained during the flatteningoperation. The appara- 113 1 18 V tus includes means for deforming theflats on the striptype tubing and means for restraining the edges of the1 1 References Cited flats during the deforming operation. The resultingtu- UNITED STATES PATENTS bular passageways have a polyhedral crosssection L394 3/1934 which is adapted to be bonded to the flat type fin190,494 M940 stock. The resultant tubing and heat exchangers 2341 95 31953 formed of the tubing is also part of the invention. 2,848,2008/1958 5 Cl 13 D 2,920,380 l/l960 W1lliams et a1. 29/1573 v rawmg gumsMETHOD OF RESHAPING PASSAGEWAYS IN METAL STRIP-TYPE TUBING This is adivision, of application Ser. No. 122,607, filed Mar. 1, 1971, nowabandoned.

BACKGROUND OF THE INVENTION This invention relates to a method andapparatus for forming metal strip-type tubing and, preferably, sheetmetal tubing suitable for use in applications, such as condensers forautomobile air conditioners. The tubing produced by this method is alsopart of this invention.

Condensers for automobile applications generally comprise a plurality ofpasses of tubing wound in a serpentine configuration with flat type finstock bonded to the tubing surfaces of adjacent passes. In order to havesufficient contact between the tube surfaces and the flat fin stockextrusions have generally been used which have a comparatively flatsurface.

SUMMARY OF THE INVENTION In accordance with this invention, metal tubingin the form of strip, preferably, sheet metal tubing having a pluralityof inflated longitudinally extending tubular passageways is employed;however, the surface of this tubing is not sufficiently flat to obtainthe necessary contact area between the fin stock and the tubing.Therefore, in accordance with this invention, a first surface and anopposing surface of the tubular passageways in the metal strip-typetubing are flattened to create more contact area between flat type finstock and these surfaces. The flattening is accomplished by passing themetal strip-type tubing between a deforming means, such as rolls whichare spaced apart an amount less than the diameter of the tubularpassageways while simultaneously restraining the edges of the strip inorder to provide adequate tube heights.

If the tubular passageways are flattened by merely passing them betweenflattening rolls without restraining their edges, the tube heights aresubstantially decreased. The extent of tube height decrease is so greatthat the tubing may not be bent without a severe pressure drop occurringin the bend areas due to the collapsing of the tubes during bending. Onemanner of overcoming this problem is exemplified by the skip flatteningtechnique described and claimed in applicants copending US. applicationSer. No. 1 19,600, filed Mar. 1, 1971, now Pat. No. 3,712,372, andassigned to the assignee of the instant invention. In accordance withthat technique the tubular passageways in the area of the bends are notflattened, thereby leaving sufficient tube height to avoid pressuredrops.

In accordance with this invention, the edges of the metal strip-typetubing are restrained while it is being flattened. Thereby, it ispossible to obtain tubular passageways having sufficient tube height tosubstantially reduce pressure drops in bend areas while providing flatsurfaces for the attachment of fins. The process of the instantinvention tends to square up the cross section of the tubularpassageways although they retain a generally six sided polyhedral shape.The invention is also directed to the tubing heat exchanger produced bythis process and the various apparatus embodiments which may be used tocarry out the process.

It is accordingly an object of this invention to provide a process forflattening a first surface and an opposing surface of at least onetubular passageway in a metal strip-type tubing, preferably a sheetmetal tubing.

It is a further object of this invention to apply this process to longlengths of such tubing.

It is a further object of this invention to provide a strip-type metaltubing and heat exchanger having a plurality of tubular passagewayswherein each tubular passageway has a first deformed flat surface and anopposing deformed flat surface and a polyhedral cross section.

It is a further object of this invention to provide an apparatus forflattening a first surface and an opposing surface of the two tubularpassageways in a metal striptype tubing while retaining sufficient tubeheight for use in heat exchange applications.

Other objects and advantages will become apparent to those skilled inthe art as a detailed discussion of particular embodiments proceeds withreference to the drawings which form a part hereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective viewillustrating the process for forming the sheet metal strip-type tubingpreferably employed with this invention.

FIG. 2 shows a perspective view of strip-type tubing having fullyinflated tubular passageways.

FIG. 3 shows a perspective view of a strip-type tubing in accordancewith this invention.

FIG. 4 is a perspective view of the typical condenser application of thetubing produced by the instant invention.

FIG. 5 is a perspective view illustrating the effect of roll flatteningstrip-type tubing without restraining the strip edges.

FIG. 6 is a perspective view illustrating the effect of roll flatteningstrip-type tubing while restraining the strip edges.

FIG. 7 is a front view of an apparatus employing the roll configurationof FIG. 6.

FIG. 8 is a perspective view of an alternative embodiment for an edgeguide in accordance with this inventlon.

FIG. 9 are sectional views of alternative roll configurations usefulwith this invention.

FIG. 10 is a perspective view of a modular roll configuration usefulwith this invention.

FIG. 11 is a perspective sectional view of a modular disk useful in theroll configuration of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand especially to FIG. 1, there is illustrated a composite metal strip 1which is used to form the preferred starting material for thisinvention. The strip 1 may be fabricated by the method disclosed in US.Pat. No. 2,690,002, granted to Grenell on Sept. 28, 1954. While thisinvention will be described with reference to sheet metal strip-typetubing, it is broadly applicable to most types of strip-type tubmg.

Referring to FIG. 1, a pattern of weld-inhibiting or stop-weld material2 is applied to a clean surface of a first strip 3 of metal. A secondstrip of metal 4 having a clean surface is superimposed on the surfaceof the first strip 3 as shown and the two strips are secured together toprevent relative motion therebetween.

Thereafter, the two superimposed strips 3 and 4 are pressure weldedtogether as by rolling so that the adjacent areas 5 of the strip 1 whichare not separated by the stop-weld material become bonded together. Therolling of the strips 3 and 4 results in reducing their thickness and inelongating the resulting strip 1 in the direction of rolling while thewidth of the strip 1 re mains substantially the same as the initialwidth of the strips 3 and 4.

Following the rolling operation, the resultant strip 1 is usuallysoftened, as by annealing, to make it more pliable. If desired, it maybe further rolled to the final gage and again softened, as by annealing.The stop-weld material results in the retention of unwelded portions 6corresponding to the stop-weld pattern 2 which are sandwiched betweenthe outer surfaces of the strip 1.

After softening the strip 1, the unwelded portions 6 are usuallyexpanded to obtain the inflated strip as shown in FIG. 2 havingpassageways 7. The expansion is obtained by injecting a fluid, such asair, water or oil under pressure of sufficient magnitude such as 500 to4000 psi to permanently deform the strip 1 in the area of the unweldedportions 6 to form the desired passageways 7.

It is preferred that the invention be carried out under tension inaccordance with the teachings of US. Pat. No. 3,538,577, granted Nov.10, 1970, to M.P.OMalley, and assigned to assignee of the instantinvention.

The pattern of weld-inhibiting material may be formed by any desiredtechnique. It is preferred to use the process disclosed in US.application Ser. No. 723,055, filed Apr. 22, 1968, by N. A. Keith, nowabandoned and assigned to the assignee of the instant invention.

The weld-inhibiting material itself may be any of the variousconventionally used materials such as graphite or titanium dioxide basedstop-weld compositions.

The process disclosed in US. application Ser. No. 7,729, filed Feb. 2,1970, by N. A. Keith, now abandoned, and assigned to the assignee of theinstant invention is further illustrative of the processes which may beused to obtain the sheet metal strip for inflation into the tubinguseful with this invention. As disclosed therein, the strip may beinitially formed as part of a wide sheet which is later slit intostrip-like material which may be coiled for further use.

It is to be understood that the above described methods of forming thesheet metal strip-type tubing useful with this invention are onlyexemplary and that other methods may be employed in the manufacture ofthe strip. The strip material made by the processes disclosed above orother suitable processes is usually employed in very long lengths.Further, the strip-type tubing may contain any desired number of tubularpassageways of any desired diameter, as may be required for achievinggiven flow and heat transfer rates.

In accordance with the instant invention a strip-type tubing 1 as shownin FIG. 3 is produced preferably in the form of very long lengths. Asshown therein, the tubular passageways 7 have flattened surfaces 8 towhich may be affixed flat type fin stock.

In FIG. 4, there is illustrated the application of the tubing 1 producedin accordance with this invention. As shown therein, the tubing 1 hasbeen bent in a serpentine configuration and flat fin stock 10 has beenaffixed to the tubing 1 between adjacent passes II. The

flat fin stock 10 is commonly affixed by means of brazing or solderingso that a bond having good heat transfer qualities is obtained. The finstock 10 is therefore bonded to the flattened surfaces 8 of adjacentpasses 1 1.

If the strip-type tubing 1 of FIG. 2 were employed in the configurationof FIG. 4, there would be unsufficient contact between the tubing 1 andthe fin stock 10 to obtain adequate heat transfer properties. Therefore,it is necessary to increase the contact area between the fin stock 10and the tubing 1 as by roll flattening in accordance with thisinvention.

When the strip 1 of FIG. 1 is inflated to form the metal strip-typetubing 1 of FIG. 2, the width of the strip decreases as the height ofthe tubular passageways 7 increases. If the tubing 1 of FIG. 2 isflattened between rolls R, as shown in FIG. 5 or otherwise, withoutrestraining the edges 12 of the strip, there is a severe reduction intube height 7. If the edges 12 are not restrained, the width of thestrip 1 tends to increase as the first and opposing surfaces of thetubular passageways 7 are flattened. Such a procedure does provide metalstrip-type tubing with flattened tubular passageways, however, the tubeheights are substantially reduced. Upon bending the strip into aserpentine configuration as in FIG. 4, there is a further intolerablereduction in the tube height in the bend areas. The collapsing of thetubes in the bend areas increases the pressure drop substantially overthat of the original tubing.

In accordance with this invention, as shown in FIG. 6, the edges 12 ofthe metal strip-type tubing 1 are restrained during the flatteningoperation so that the width of the strip 1 cannot increase. By adoptingthis approach, there is considerably less reduction in the tube heights7 as compared to carrying out the process without restraining the edgesas in FIG. 5.

The tubing 1 as shown in FIG. 3 obtained by the method and apparatus ofthis invention has the desired flattened surfaces 8 with a small butgenerally acceptable reduction in tube height 7 The cross section of thetube 1' as shown in FIG. 3 reveals that the tubular passageways 7 havebeen substantially squared up. The passageways generally have what maybe described as a polyhedral cross section. The polyhedron usuallyappears as a six sided figure with the sides 8 which contact the finstock being wider than the adjoining sides S.

The diameter of the tubular passageways 7' in the metal strip may be asdesired to meet a given application. However, for condenserapplications, it has been found that a diameter between about 0.175 and0.250 inch is most useful with a preferred range between about 0.200 and0.230 inch. Generally, there is a reduction of between 0.020 and 0.060inch in the tube height following roll flattening in accordance withthis invention. Preferably, the reduction in tube height is between0.040 and 0.050 inch. The width of the flat formed on the tube varieswith the tube diameter and the amount of reduction in tube height. Forthe preferred tube diameter of 0.230 inch, a reduction in tube height of0.020 inch and 0.060 inch will generally yield a flat having a widthbetween 0.075 inch and 0.125 inch. Preferably, for this size tubing, theflat is around 0.100 inch.

While the above ranges are specific to tubing especially adapted for usein condenser applications, the invention is broadly applicable to anytype of metal striptype tubing having any given diameter of tubularpassageways.

FIG. 6 is exemplary of a roll configuration suitable for carrying outthis invention. The configuration 20 comprises flattening rolls 21 whichare spaced apart a distance less than the diameter of the inflatedtubular passageways 7 in the metal strip-type tubing 1 which is thestarting material of this invention. The configuration 20 also includesedge guide rolls 22 which restrain the edges 12 of the strip 1 to keepit from spreading during the flattening operation.

The roll configuration 20 of FIG. 6 may be employed using an apparatussimilar to that shown in FIG. 7. The apparatus 30 comprises a frame 31.One of the flattening rolls 32 is rotatably mounted to the frame 31, theshaft extension at 33 being connected to a suitable gear drive (notshown) which are known in the art. A second flattening roll 34 isrotatably mounted within a movable carriage 35 which has shafts 36 whichpass through the frame 31. The carriage is spring biased at 37 withrespect to the frame 31 so that sufficient pressure is applied to theroll 34 to do the flattening. The height of the roll 34 and, thereby,the distance between flattened rolls 32 and 34 is adjusted by means ofnuts 38 which may be tightened or loosened about the threaded shafts 36.As with the other flattening roll 32, this flattening roll 34 has ashaft 39 extending out from the frame 31 which is connected to asuitable gear drive mechanism (not shown). The hole 40 in the frame 31through which this shaft 39 passes is elongated to provide for travel ofthe roll 34.

The edge guides 42 in the apparatus of FIG. 7 comprises rolls 42 and 43.The edge guide roll 42 is rotatably mounted to the frame 31. The roll 43is held within a movable carriage 44 which moves within a hole in theframe 31. The carriage 44 has flanges 45 with holes which pass aboutthreaded shafts 46 mounted to the frame 31. Spring biasing 47 and nuts48 are used to provide adjustment of the distance between the edge guiderolls 42 and 43.

In using the apparatus 30 of FIG. 7, the distance between the edgeguides 42 and 43 is adjusted to substantially equal the width of thestarting metal strip-type tubing 1. The distance between the flattenedrolls 32 and 34 is adjusted to give the desired amount of flattening.Then the strip 1 of the type shown in FIG. 2 is fed into the apparatus.The emerging strip 1' from the apparatus 30 is of the type shown in FIG.3.

The apparatus 30 shown in FIG. 7 is but one configuration that may beused. The specific design of the mill itself, other than the rollconfiguration and means for restraining the strip edges 12 isconventional and forms no part of the invention herein. The way in whichthe rolls 32 and 34 are mounted and the adjustments provided for themmay be done in any conventional manner and FIG. 7 is merely illustrativeof one apparatus which could be used.

Thus far, the edge guides 42 and 43 have been described in the form ofrolls. It is also possible to use edge guides as shown in FIG. 8. Thisedge guide 50 is not rotatable but rather the strip 1 engages it bysliding within the slot 51. The body 52 of the guide is shaped similarto the edge guide carriage 44 in FIG. 7. The operative surface of theguide contains a slot 51 which engages the edge 12 of the strip 1. Asimilar type of edge guide 50 could be used in place of the edge guideroll 42 on the other side of the apparatus 30.

In the apparatus of FIG. 7, the flattening rolls 32 and 34 were of asimple cylindrical shape and, therefore, edge guides 42 and 43 wererequired as aforenoted to restrain the strip 1 edges to maintainadequate tube heights. Other roll shapes could be used which wouldeliminate the need for edge guides. i

In FIG. 9A, there is shown a roll configuration wherein the upperflattening roll has deep flanges6l between which the metal strip-typetubing 1' rides. These flanges 61 act in the same manner as the edgeguides 42 and 43 in the apparatus of FIG. 7. The bottom flattening roll62 has a width which is adapted to fit between the flanges 61 of theupper flattening roll 60. In operation, the flanges 61 of theupperflattening roll 60 restrain the edges of the metal strip-typetubing 1 while the hub surface 63 of the upper flattening roll 60 coactswith the surface 64 of the lower flattening roll 62 to provide theflattening action.

In FIG. 9B, a still more preferred embodiment is shown. In thisembodiment, both flattening rolls are identical and each has flangeportions 71. Opposing flange portions 71 clamp the edge of the sheetmetal strip-type tubing 1' as it is being flattened between the hubportions 72. The engagement. between the flanged portions 71 of theflattening rolls 70 and the edges of the strip-type tubing 1 providesthe restraining action required in accordance with this invention.However, because only the outer edges of the strip-type tubing 1 areclamped, there tends to be a greater squaring up of the outer tubes 73as compared to the inner ones 74. To overcome this effect, the rolls ofFIG. 9C were designed.

In the configuration of FIG. 9C, both rolls are identical and each rollhas flange portions 81 which clampingly engage each of the weldedportions 82 of the composite metal strip-type tubing 1. In this manner,each of the tubular passageways is squared up substantially the sameamount.

The alternative embodiments for the roll configuration shown in FIGS. 9Ato 9C could be made in one piece as is common in the art, or they couldbe assembled from a plurality of pieces in a manner similar to theassembly in slitting knives used in the slitting art. In accordance withthis aspect of the invention, the flattening rolls are assembled from aplurality of disks on a shaft 91 having a key way 92 as shown in FIG.10. Each disk 90 as shown in FIG. 11 is cylindrical in nature and has ahole 93 of a diameter adapted to fit about the shaft 91. Each disk 90further has a key-type protrusion 94 extending into the hole and adaptedto engage the key way 92 of the shaft 91.

As shown in FIG. 10, taking the configuration of FIG. 98 as an example,the flange portions 71 could comprise disks 90 of a different diameterthan the hub portion 72. The width W of the hub portion 72 could bevaried by increasing or decreasing; the number of disks 90 present init. One could obtain the configuration of FIG. 9C to merely insertingfurther disks 90 of larger diameter at the appropriate positionsalongthe hub portions 72. This approach of using cylindrical disks 90 toform the desired roll configuration is preferred because of theflexibility it gives in. changing from one width of strip 1 to anotherand from one diameter tubing to another, and in changing between striphaving different numbers of passageways.

In the embodiment discussed thus far, the flattening of the metalstrip-type tubing was obtained by means of roll deforming. However, theflats could be obtained by other methods of deforming the surface as,for example, by compressing the strip in a press or by swaging the stripor hammering the flats. The essential element, however, is that somemeans must be included in any apparatus for restraining the edges of thestrip so that the strip width cannot increase as the tubular surfacesare flattened. The embodiments discussed employing roll deforming,however, are the most preferred and economical approach toward carryingout the instant invention.

Sheet metal strip-type tubing shown in FIG. 2 is preferred as thestarting material of this invention. The invention, however, is broadlyapplicable to any type tubing including extruded type tubing having ashape similar to that of the tubing of FIG. 2.

The tubing is generally formed of steel, copper, copper alloys and,preferably, aluminum and aluminum alloys.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare suitable of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within the spirit and scope as defined bythe claims.

What is claimed is: l. A process of reshaping passageways in a metalstrip-type tubing adapted to be used in a heat exchanger comprising:

providing a metal strip-type tubing having at least one previouslyinflated tubular passageway;

flattening a first surface and an opposing surface of said at least onetubular passageway, and simultaneously restraining the edges of saidmetal striptype tubing to prevent the tubing from increasing in widthwhereby the shape of the passageway is modified but the length of thetubing is substantially unchanged.

2. A process as in claim 1 wherein said strip-type tubing has aplurality of tubular passageways.

3. A process as in claim 2 wherein said strip-type tubing is formed ofat least two strips of metal pressure welded together in parts.

4. A process as in claim 3 wherein said flattening is performed bydeforming said strip between a pair of spaced apart rolls.

5. A process as in claim 2 wherein the strip-type tubing has a thicknessbetween passageways which is substantially twice the thickness of thepassageway walls. =I =l

1. A process of reshaping passageways in a metal strip-type tubingadapted to be used in a heat exchanger comprising: providing a metalstrip-type tubing having at least one previously inflated tubularpassageway; flattening a first surface and an opposing surface of saidat least one tubular passageway, and simultaneously restraining theedges of said metal strip-type tubing to prevent the tubing fromiNcreasing in width whereby the shape of the passageway is modified butthe length of the tubing is substantially unchanged.
 2. A process as inclaim 1 wherein said strip-type tubing has a plurality of tubularpassageways.
 3. A process as in claim 2 wherein said strip-type tubingis formed of at least two strips of metal pressure welded together inparts.
 4. A process as in claim 3 wherein said flattening is performedby deforming said strip between a pair of spaced apart rolls.
 5. Aprocess as in claim 2 wherein the strip-type tubing has a thicknessbetween passageways which is substantially twice the thickness of thepassageway walls.